Method of making a bonded nonwoven web of staple-length filaments



March 10, 1970 as. WAG E 3,499,810

METHOD OF MAKING A BONDED NONWOVEN WEB OF STAPLE-LENGTH FILAMENTS FiledMay 31, 1967 3 Sheets-Sheet 1 POLYMER SPINNING AND COLLECTION OFFILANENTS.

FILANENTARY TOW CONERENT RIBBON CRINPINC OF 4 HLM'ENTS' TRANSVERSE OUTTINC.

CRINPEO FIBROIJS FILANENTARY TOW SECTIONS OERECISTERING OF CAROINC/FILMIENT E ]5 REDISTRIBUTIONM 1 CRIHPEO UNBONOEO DERECISTEREO HBROUSFILANENTARY TON ASSEMBLY ANNEALINC 0F HLAIEHS' NEAT ANO COOL ANNEALEO,CRINPED BONDED OERECISTEREO uobwov FILANENTARY TON LON-NELTINC COMPONENTAPPLIED BY INVENTOR DIPPING. OINMR CANPAT OLE ATTORNEY March 10, 1970 o.e. WAGLE 3,

METHOD OF MAKING A BONDED NQNWOVEN WEB STAPLE OF -LENGTH FILAMENTS FiledMay 31, i967 3 Sheets-Sheet 2 FIIG.Z

CONTINUOUS- LENGTH BONDED RIBBM cumzn sEcnous UNBONDED PI ow T I HBROUSI LL ICKNG ASSEMBLY STRUCTURAL FIBERS F I 6- 3A FABRIC LOIER HELTINGCOMPONENT F l G- 4 FUSION BOND-LOWER HELTIHG COMPONENT INVENTORSTRUCTURAL FIBER 0mm mm mm @0444?! Q IM ATTORNEY March 10, 1 97 0 0; a.WAG LE 3 499.810

METHOD (OFMAKING 'A BONDED NONWO-V-EN WEB 0F STA LE-LENGTH FILAMENTSFiled May 31, 1967- I 3 Sheets-Sheet. 5

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' DRYER -4 L AIR TO SOLVENT RECOVERY CONTINUOUS LENGTH R BONDED RIBBIONANNEALED, ORINPEO OEREOISTEREO FILANENTARY TOI MR FROII SOLVENT RECOVERYINVENTOR DINKAR GANPAT WAGLE BY QM ATTORNEY United States Patent3,499,810 METHOD OF MAKING A BONDED NONWOVEN WEB OF STAPLE-LENGTHFILAMENTS Dinkar Ganpat Wagle, Wilmington, Del., assignor to E. I. duPont de N emours and Company, Wilmington, Del., a corporation ofDelaware Continuation-impart of application Ser. No. 554,582, June 21,1966. This application May 31, 1967, Ser. No. 646.146

Int. Cl. B32b 31/00; D04h 3/16 US. Cl. 156152 6 Claims ABSTRACT OF THEDISCLOSURE CROSS REFERENCES TO RELATED APPLICATIONS This application isa continuation-in-part of my application Ser. No. 554,582, filed June21, 1966, now abandoned.

BACKGROUND OF THE DISCLOSURE Field of the invention This inventionrelates generally to the preparation of a high bulk, thermallyself-bonded, fibrous product and to an unbonded assembly of crimped,stabilized filaments useful as an intermediate for the productionthereof. More particularly, the present invention relates to a processembodiment leading to such products and intermediates.

Description of the prior art Various procedures have been developed inrecent years involving the utilization of so-called fiber-fill in theprovision of bonded fibrous batts, webs and other nonwoven products ofthe bulky type suitable for quilted fabric interliners, pillow-fillingsand the like. Perhaps most notable among these procedures is thatinvolving the preparation of a batt for the fiberfill and subsequentspraying of the batt with an adhesive to bond the filaments into acoherent structure. While such structures have achieved some degree ofimportance in the textile industry, numerous processing problems andproduct limitations have nevertheless arisen. In the first place thesemethods use spraying equipment and this is particularly disadvantageousin that a nonuniformly bonded product is obtained. Even when a thinarticle such as a web is to be produced, a substantially greaterbuild-up of binder occurs on the surface than does on the inside andthis inefficient utilization of binder detracts from softness or otheraesthetically desirable properties and is, of course, uneconomical. Forthicker webs or batts, there is a practical limit of thickness beyondwhich it is difficult to obtain any degree of penetration of binder intothe middle thereof, at least without greatly overloading the structurewith binder. Yet inadequate or nonuniform bonding throughout thestructure may result in inadequate strength or inferior compressionalproperties.

SUMMARY OF THE INVENTION In accordance with the invention there isprovided an unbonded assembly, having a density of up to about 13,499,810 Patented Mar. 10, 1970 lb./ft. of crimped, individuallydistinct staple-length filaments which have been so prepared that onceformed into a desired shape, a brief exposure to heat will result in auniformly bonded product. The assembly has the advantages of fiberfillbut in addition is self-bondable. The need for spraying the nonwovenassembly is obviated because the binder is pre-afiixed to the filaments.Moreover, the binder is evenly distributed throughout the filaments,hence can be used more sparingly to give property advantages while atthe same time affording superior product uniformity. Still a furtheradvantage of the assembly is that the fibers become strongly adhered toone another by fusion bonds, yet the filaments have been prestabilizedso that the assembly will undergo little or no densification during thebonding step.

The thermally self-bondable assembly of crimped, individually distinct,staple-length filaments is provided by a process comprising the steps of(1) collecting into a continuous length bundle a plurality of filamentscomprising an oriented filamentary component of-a fiberforrning,synthetic, organic polymer, (2) crimping said filaments to provide anaverage crimp frequency of at least 3 crimps per inch and an averagecrimp index of at least 5%. (3) separating the crimped filaments fromone another, (4) applying to said crimped, separated filaments, withoutsubstantially removing crimp therefrom, a coating of a lower-meltingsynthetic thermoplastic polymer component to thereby provide acontinuous'ribbonlike structure, said lower-melting component having apolymer melt temperature which is at least 70 C. but is below the fiberstick temperature of the filamentary com-1 throughout the threedimensions thereof an essentially constant weight ratio of saidfilamentary component to' said lower-melting component, (7) itbeing--further:pro-

vided that at least prior to the preparation of said lowdensity assemblyof step (6), above,- said filamentary component is annealed at anelevated temperature in a substantially relaxed state to provide amaximum retractive coefiicient of about 30.

In effect the fibrous assembly so obtained is ready for bonding; thatis, (a) the heat-activatable binder or socalled lower-melting componenthas alreadybeen applied, (b) the filaments have been crimped-to'-provide bulk and/ or other properties, (0) the filaments have beenstabilized (hence have a low retractive coefiicient as hereinafterdefined) to minimize latent shrinkage or crimpability forces that mighttend to excessively density the product upon bonding, and (4) thefilaments have been redistributed, i.e. nearly all filament-to-filamentbonds broken up and the filaments blended to a highly uniformlow-density mass, e.g. below 1 lb./ft. usually as low as 0.6 lb./ft. oreven 0.1 lb./ft. In order to make a thermally self-bonded, low-density,nonwoven product it is merely necessary to heat the unbonded assembly,prepared as described, to a'= temperature in excess of said polymer melttemperature but below said fiber stick temperature, then cool to bondthe filaments.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a flow diagram of varioussteps, in one sequence, leading to the unbonded fibrous assembly andthen to the bonded nonwoven product.

FIGURE 2 shows schematically the ribbon cutting step of FIGURE 1 inwhich fibrous sections are produced.

FIGURE 3 shows schematically a pillow in which a fabric ticking has beenstuffed with an unbonded fibrous assembly of the invention.

mechanically dis- FIGURE 3A shows schematically an enlarged view of theencircled portion of FIGURE 3. As shown in FIG- URE 3A individualfilaments have a discontinuous coating of low melting component thereonbut are not bonded to one another.

FIGURE 4 shows schematically an enlarged view of the filamentarystuffing of FIGURE 3 after bonding,

FIGURE 5 shows schematically one form of a tow coating procedure.

DETAILED DESCRIPTION Composition of the polymeric components Asindicated above, the unbonded assembly of the invention utilizes twocomponents, structural filaments and a heat-activatable adhesivereferred to herein as the lowermelting component. The filaments comprisean oriented, filamentary component of a fiber-forming, synthetic,organic polymer having a relatively high fiber stick temperature. Thelower-melting component comprises an unoriented synthetic thermoplasticpolymer and it has a polymer melt temperature which is at least 70 C.but is below the fiber stick temperature of the filamentary component.

The filaments employed are commonly available synthetic polymerfilaments of the type produced by spinning and drawing. Normally, thefilaments may have a denier within a wide range, for example, from 1 to50 denier per filament. Frequently, however, the most desirableaesthetics, e.g. softness, are achieved in bonded nonwoven products madefrom filaments having a denier in the range of approximately 1 to 15denier per filament. The cross-section of the filaments will normally beround, but may be prepared so that it has other cross-sectional shapes;such as elliptical, trilobal, tetralobal, and the like shapes.

The filamentary component may comprise a variety of synthetic, organicpolymers, such as polyolefins, acrylonitrile polymers and copolymers,polyesters, polyamides, vinyl polymers and copolymers, polyurethanes,polyformaldehyde, cellulose acetate and the like. It should have eithera higher polymer melting temperature than the lower-melting bondablecomponent, or should be of such a character that it has high heatstability and can be regarded as having no melting or softening pointunder ordinary use conditions. The general term fiber stick temperatureis accordingly used. The filamentary component need not be thermoplasticbut must be of fiberforming molecular weight.

By synthetic polymer is meant a material synthesized by man asdistinguished from a polymeric product of nature. The class of syntheticpolymers, thus excluding for example cotton and viscose rayon, hasseveral advantages for cushioning applications over polymers of nature.They generally have a high elastic recovery; this being defined as theamount by which a fiber recovers after application and removal of aforce (stress) causing deformation. Synthetic fibers usually show anelastic recovery of 90- 100% from 2% extension as compared to, forexample, as little as 74% for cotton. The synthetic polymers as a classalso generally exhibit superior resistance to stress decay and lowermoisture regain properties.

The second or lower-melting component should comprise a thermoplasticpolymer and have a polymer melt temperature above about 70 C. but belowthe fiber stick temperature of the filamentary component. This willensure, first, that thermal bonding can occur without destroying thefilamentary component, and, second, that the bonds will not be destroyedby moderately high temperatures of the kind normally experienced duringuse, i.e. usual laundering and drying procedures. Preferably, thepolymer melt temperature of the lower-melting component will be within 5to 50 C. of the fiber stick temperature of the filamentary component tofacilitate the thermal bonding procedure.

The lower-melting component is lateritly bondable such that uponfabrication of the filaments into the form of the desired fibrousassembly, e.g. a batt or web, mere application of heat will cause thiscomponent to soften and/or melt. Upon cooling, bonds will thus be formedwith neighboring fibers, whether or not the latter contain a bondablecomponent associated therewith. Thus it is frequently desirable toincorporate ordinary staple filaments, either of natural fibers or ofsynthetic fibers, in the fibrous assembly.

The lower-melting component may be selected so that it is fiber-forming,and normally this would be the case. On the other hand, it can also benon-fiber-forming, e.g. be a polymer of relatively low molecular weight.Typical thermoplastic polymers which can be used as the lowermeltingcomponent include polyolefins, acrylic resins, acrylic terpolymers,polyesters and copolyesters, polyamides and copolyamides, vinyl polymersand copolymers and the like.

For some applications it is desirable that the filaments of the assemblybe provided with only small amounts, i.e. less than 15% by weight, ofthe lower-melting component in order to achieve certain properties suchas softness of hand in the final bonded product. For other applicationsas much as 50% by weight or more of the lower-melting component may beused.

In a preferred embodiment of the invention the filamentary component andthe lower-melting component will be derived from the same chemical classof polymers, for example, a polyester such as polyethylene terephthalatewill be used to form the filamentary component whereas the lower-meltingcomponent will comprise a copolyester such as the copolymer of ethyleneglycol with a mixture of isophthalic and terephthalic acids. Polyamidesand copolyamides may similarly be used to advantage. The utilization ofchemically related polymers in this manner is especially desirablebecause it gives rise to interfilament bonds of a particularly highadhesion level.

Either or both of the components may include conventional additives suchas dyes, pigments, U.V. stabilizers and antistatic agents.

Preparation of unbonded assembly and bonded nonwoven In accordance withthe invention, a supply of filaments is obtained by any of the usualprocedures of dryspinning, wet-spinning 0r melt-spinning a fiber-formingsynthetic organic polymer. Upon issuing from orifices of a spinneretinto a quenching chamber the filaments are collected and drawn in theusual way. The drawing of the filaments serves to orient the polymermolecules and to provide strength and other properties. Conveniently,filaments will be obtained from a series of spinnerets, thereaftercollected together into a continuous bundle of substantiallyparallelized filaments, e.g. a so-called tow and then drawn. As isfrequently the case with freshly-drawn filaments, they may be annealedto some extent, e.g., heated above their second-order-transitiontemperature while substantially relaxed, following the drawingoperation.

The tow of filaments may then be subjected to a crimping operation bytechniques known in the art. Typical among the mechanical crimpingdevices which may be employed for this purpose is the co-called stufilngbox type of crimper which normally produces a zig-zag crimp.Alternatively, there may be used apparatus employing a series of gearsadapted to apply a gear crimp continuously to a running bundle offilaments. Certain types of filaments can also be crimped other than bymechanical means, for example polyethylene terephthalate fibers may beprovided with a helical crimp by the air quenching procedure describedby Kilian in US. Patent 3,050,821. In this instance the crimping stepis, in effect, performed concomitant y with the spinning operation andseveral bundles of crimped filaments are then combined to form the tow.In any case the crimped filamentary tow so produced may be a highlycompacted product in which many of adjacent filaments are in phase withone another, i.e., pairs or groups of crimped filaments contact oneanother for substantial distances along their lengths. Accordingly it isgenerally necessary to thereafter treat the tow of crimped filaments insome manner to separate adjacent filaments from one another, i.e. soadjacent filaments touch only at spaced points. Advantageously this maybe effected by deregistration in which adjacent filaments are renderedout of phase with one another.

For purposes of filament separation there may be used various devices ofthe kind commonly employed in the tow-treating art. In one of these thetow is subjected to an explosive expansion of compressed air using aspecially adapted venturi nozzle as described in Caines et al. US.Patent 3,099,594. An alternate technique for separating andderegistering filaments of a crimped tow involves the use of rollsprovided with a series of rigid surfaces with serve as gripping meansfor displacing filaments relative to one another. Apparatus of this typeis illustrated in Mahoney et al. US. Patent 3,032,829 and in Dunlap etal. US. Patent 3,156,016. Still another form of apparatus which may beused for this purpose is that illustrated in Jackson US. Patent2,929,392 involving the use of pairs of rolls to first straighten thecrimped filaments and then to suddenly relax the tow and thereby effectblooming.

The particular type of crimp, i.e. in terms of its dimensionalcharacteristics, is not critical but rather can be selected dependingupon the type of textile product to be ultimately formed. Thus the crimpmay be essentially planar or zig-zag in nature or it may be athreedimensional crimp. Whatever the nature of the crimp, the filamentsshould attain an average crimp frequency of at least 3 crimps per inchand an average crimp index of at least 5%.

The tow may vary widely in terms of its cross-sectional dimension andthe number of filaments therein. Thus a bundle may be used wherein thenumber of filaments is in the range of 500 to 5,000,000.

Once the crimped and separated filamentary tow is produced, it may thenbe annealed at this stage to reduce the so-called retractive coefficientto a suitably low level, i.e. so that it is not in excess of about 30.The low retractive coefiicient indicates that the filamentary componenthas been treated at some stage of its processing to remove most, if notall, of the latent crimping and shrinkage forces therefrom. During asubsequent 0 thermal bonding treatment the individual filaments willundergo little or no relative movement or other dimensional change andthus compaction and densification of the assembly will be greatlyminimized. Preferably, the retractive coeflicient will be as close tozero as possible, i.e. up to or so, to ensure only very modestdensification during the thermal bonding treatment. In effect, theretractive coefficient expresses a relationship between the length ofthe filaments before and after they are exposed to a temperature abovethe polymer melt temperature of the lower-melting component but belowthe fiber stick temperature of the filamentary component.

Continuous textile strands as initially prepared may have a relativelyhigh retractive coefficient. This is a result of drawing treatmentsperformed subsequent to the spinning operation in order to reduce thedenier of the spun filaments and to develop strength or otherproperties. The drawing treatment creates internal stresses within thefilaments and these often tend to result in undesirably high levelshrinkage and/or crimping forces should the filaments be heated abovetheir second-order transition temperature, i.e. of the filamentarycomponent. In accordance with the invention the filaments arestabilized, e.g., by annealing, to relieve these tendencies and thuslower the retractive coefficient. A low-density nonwoven batt can thenlater be prepared in which the filaments will undergo little or norelative movement upon heating to a bonding temperature-hence individualfilaments become merely bonded to one another in generally the samelow-density configuration as existed in the unbonded assembly andfilament intertwining or entanglements are kept at a minimum. Of course,the actual percent bulk loss in bonding can vary depending upon suchfactors as the unbonded batt density, filament denier, retractivecoefficient level, etc.

For purposes of annealing the filaments, a temperature will normally beselected which is above the second-ordertransition point of thefilamentary component but below its fiber stick temperature. Althoughthe annealing temperature selected will depend upon the composition ofthe filamentary component, usually it will exceed C. Hot air, hot wateror steam may be used depending upon the type of filament. Normally, afew seconds or minutes of exposure at such a temperature is sufiicientfor annealing the filaments of the tow to remove the latent crimpabilityand shrinkage forces before further processing of the filaments.Individual filaments are, of course, under essentially no externallyapplied tension during the annealing step. If the filaments are of atype which develop crimp upon heating, then crimping and annealing maybe effected simultaneously.

The annealed tow of crimped, separated filaments may be then coated toform a coating of lower-melting component along the exterior of thefilaments. Spraying or dipping procedures may be used for this purposeand the resulting product will thus be bonded into an integralribbon-like structure. The bonds are adhesive bonds as contrasted to thefusion bonds to be created upon later heating the coated filaments to abonding temperature. The adhesive bonds so obtained will beintentionally broken at later stages of processing as the filaments areredistributed to form a uniform assembly. The advantage of coating thefilaments following steps of crimping and deregistration is that theadhesive bonds occur mostly at spaced points rather than as continuouslengths of bonding areas which would be dilficult to break in subsequentprocessing.

The bonded ribbon-like structure is obtained, in one embodiment, bycausing a running length of the previously prepared tow to bemomentarily immersed in a solution or dispersion of the lower-meltingcomponent. The choice of the solvent or other vehicle for this purposeis not critical, but, of course, it should be a nonsolvent for thefilamentary component. Volatile inert liquids such as water, alcohols,esters, hydrocarbons, and halogenated hydrocarbons are exemplary of themany materials which can be used. Advantageously, the freshly-coated towwill then be passed through a pair of resilient, driven nip rolls tosqueeze excess solution or dispersion therefrom and to uniformlydistribute the lower-melting component therethrough. After drying,preferably below the polymermelt temperature of the lower-meltingcomponent, the coherent ribbon-like structure is obtained.

Spraying procedures may similarly be used in which a solution ordispersion of the lower melting-component is applied as a fine mist tothe tow. Hence, for ease in processing, the use of a dip coatingprocedure is preferred.

The preparation of the bonded ribbon-like structure will be described ingreater detail with reference to FIGURE 5. The annealed, crimpeddleregistered filamentary tow is guided into the dip tank 11 andcompacted to remove air by a first pair of driven squeeze rolls 12having a film sleeve thereon of polytetrafluoroethylene. The tow fromthe first pair of squeeze rolls 12 is led into and out of a solution 14of the lower-melting component as it passes about bar 13 submersed inthe solution. The tow then passes through a second series of weighted,driven squeeze rolls 15 to remove excess solution therefrom and returnit to the dip tank 11. The rolls 15 have a resilient rubber coveringprotected by a sleeve of polytetrafiuoroethylene film. The tow thenpasses through dryer 16 by means of driven guide rolls 17 as heated airfiows first, in the direction of tow travel and secondly, counterthereto. Finally the tow exits through driven squeeze rolls 18 and aboutdriven guide roll 19 to be wound up or otherwise further processed.

If the solvent for the lower-melting component is a volatile liquid suchas methylene chloride or 1,1,2-trichloroethane, as is preferred, thendrying of the tow can be effected at a high rate of speed. For example,with air heated at about 120 C. to 160 C. or so, there is almostinstantaneous drying of the tow, i.e. usually in less than about 2seconds.

As the tow passes through the vertical dryer 16, a low amount of tensionis preferably maintained on the tow to ensure that the crimped filamentsare not appreciably straightened out as the lower melting component issolidified. The retention of crimp is important during the clip coatingprocedure in order to facilitate the subsequent carding operation. Theminimum tension is provided by driving rolls 17 at a slight lower speedthan squeeze rolls 15, thus ensuring that any loss of crimp, i.e.straightening, of the filaments occurring in the dip tank 11 (because ofthe weight of solution thereon) is restored before the lower-meltingcomponent solidifies. Tension during drying should preferably not exceedabout 0.009 gram per denier. Excess tension is likewise avoided as thetow passes between rolls to minimize loss of crimp.

The amount of lower-melting component applied to the tow can be adjustedto a desired level by appropriately changing either its concentration inthe solution or dispersion, the pressure applied by the squeeze rolls,or the speed of the tow being coated.

The continuous, bonded, ribbon-like structure, above described, may varyconsiderably in its characteristics. Usually it will be relatively denseas contrasted to the high bulk nonwoven product which can later 'beformed after thermal bonding. Densities in excess of 1 lb./ft. are notuncommon for the ribbon-like structure. Its crosssectional dimensionsmay vary from a few inches, or even less, to several feet in width.Normally its thickness will only be a fraction, eg one fifth or less, ofthe width dimension. Desirably it will at most be only a few filamentsin thickness.

The coating process will result in a difference in orientation betweenthe two components. Thus the drawn filamentary component will berelatively highly oriented whereas the lower-melting component will be arelatively unoriented coating along the exterior of the filaments. Thecoating may typically be non-uniform, e.g. with varying thickness, oreven discontinuous. However, the term discontinuous is not meant toimply that the lower-melting component is necessarily in particulateform along the exterior of the filaments. Thus in fact it may be in thenature of a filmy coating covering large areas of the filaments-withdiscontinuities existing only on a microscopic scale.

The ribbon-like structure is, as a next step, reduced to a staple-lengthby cutting it at intervals transversely to its longitudinal axis, asshown in FIGURE 2. As a result, socalled fibrous sections are thusproduced, in each of these the parallel alignment of filaments ispreserved. By this operation the filaments themselves are reduced to ahighly uniform staple length. The tow may be conveniently cut by any ofthe well known types of staple cutters. The length of the fibroussections, i.e. in the direction parallel to the direction of filamentalignment, can be of ordinary stable fiber length, e.g. about 1 inch to6 inches.

As will be apparent from the foregoing, an advantageous feature of theinvention is that the above-described steps, starting with spinning andincluding that of coating, can all be performed with a continuouslyrunning tow. From the standpoint of a commercial operation this not onlyrepresents a high degree of process efiiciency, because adhesive is notapplied to individual articles, but also it affords improved productuniformity.

As a next step in the preferred process embodiment of the invention, thefibrous sections are opened and the individual staple-length filamentsdistributed; that is, separated from one another and initimatelyblended. Adhesion bonds are broken but substantial portions of thelower-melting component remain afiixed to the filaments. There is thusobtained a loose, bulky assembly of individually distinct, crimped,stabilized, coated staple filaments which throughout its threedimensions is highly uniforms in terms of the ratio of filamentarycomponent to lower-melting component. The latter characteristics, inparticular, distinguish the bonded nonwoven products of the inventionfrom attempts in the prior art to obtain bulky, adhesive coated nonwovenproducts. The essentially constant ratio of the two components meansthat bonding can also be essentially uniform such that compressional andother properties will not materially vary through the thickness of thestructure. Perhaps most importantly, the uniformly bondablecharacteristics means than a fabricator of finished textile articles canproduce a wide variety of products by the simple expedient of heatingshaped assemblies.

An ordinary card or garnett card machine is particularly suitable foreffecting mechanical redistribution of the filaments of the cut,staple-length fibrous sections. The combing action of the typical cardcloth cylinder employed therewith serves to effect rupturing of theadhesive bonds while at the same time uniformly blending the fibers to abulky fibrous assembly, e.g. in the form of a batt or web. Onceredistributed in this or other ways, the individual filaments can beformed into a product of the desired characteristics by other techniquesas well, for example batts may be processed on a Rando-Webber machine orother known air-laydown machines, i.e. a Duo-Form machine.

One advantage of this invention is that highly bulked nonwoven productscan be obtained. With such low density products it is particularlyimportant for functional purposes that the bonding be substantiallyuniform throughout. Bonded products having densities below 1.5 lbs./ft.in fact as low as 0.2 lb./ft. are readily obtainable. Moreover, only arelatively modest increase in density will have occurred during bonding.

The step of thermally bonding the unbonded fibrous assembly isaccomplished by merely heating the assembly to a temperature is excessof the polymer melt temperature of the lower-melting component. Thelatter softens or melts and, upon cooling, bonds are formed at fibercross-over points throughout the three dimensions of the structure, asindicated generally in FIGURE 4.

As above-mentioned, ordinary filaments, i.e. uncoated or monocomponentfilaments, may be blended with the coated filaments in forming theunbonded assembly. The ordinary filaments would have a maximumretractive coefiicient of 30 and a fiber stick temperature above thepolymer melt temperature of the lower-melting component of the coatedfilaments. Such ordinary filaments may comprise 0 to by weight of theunbonded assembly.

The sequence of processing steps illustrated in FIG- URE 1 and discussedabove is advantageous from the standpoint of ease and economy. However,it will be apparent that numerous variations are possible, but withincertain limits. In particular, the annealing step can be performed atany convenient stage of processing following drawing to reduce theretractive coefficient to a maximum of 30. In one respect it isadvantageous for this step to be performed after crimping and beforecoating since high annealing temperatures can then be used withoutfusing the lower-melting component. On the other hand it is alsoentirely practical to effect annealing after coating. Even if thepolymer melt temperature of the lower-melting component is exceededduring annealing and some fusion occurs, the bonds in the ribbon-likestructure can usually be broken during a subsequent mechanicalredistribution step, e.g. carding. Two or more annealing steps can alsobe used, for example one following drawing and another followingcoating. The staple cutting operation can also be performed at variousstages, although it will be apparent that coating, crimping andannealing steps are more easily carried out using a continuous filamenttow. Other such variations will also be evident.

Characteristics of the assembly and uses In one embodiment the productof the invention is an assembly of coated filaments which (a) are highlydissociated, i.e. the filaments are not thermally or adhesively bondedto one another but rather exist as individually distinct filaments, (b)are relatively highly crimped but nevertheless are stabilized so as tosubstantially prevent shrinkage and movement when subjected to a thermalbonding treatment, and (c) possess by virtue of the lowermeltingcomponent an ability to bond to themselves or to other fibers whenheated above the polymer melt temperature of that component.Advantageously, at least a major proportion by weight of the assemblyshould comprise coated filaments as above defined-but this is notessential to all uses.

As an article of commerce the assembly is suitable in widely diverseapplications. In this respect it is to be understood that the termassembly is not intended to designate any particular geometrical shapeor even any particular arrangement or size of the filamentary structurestherein, for these are aspects that can be appropriately selecteddepending upon the intended use of the assembly.

The assembly of filaments may be conveniently provided in the form of acontinuous length web of staple fibers, which can be supplied to thetextile industry for conversion into textile structures of the desiredtype, e.g. into non-woven batts, slivers, and yarns, or into knitted,tufted, and woven fabrics. For such uses the filaments of the assemblymay be blended with various proportions of ordinary staple fibers whichare not self-bondable themselves.

In one embodiment of the invention, the assembly of filaments is used toproduce a bonded block of fibers which are aligned in the samedirection. This is then sliced perpendicular to the direction of thefibers to produce porous, self-supporting fiber-on-end sheets, asdedscribed in Koller US. 3,085,922. Alternatively, the assembly offilaments may be processed on a garnetting machine and then cross-lappedto entangle the fibers into a nonwoven batt structure, which may bebonded by heating the batt above the polymer melt temperature of thelower-melting component. Nonwoven products may be formed into thin battsfor use as such or the batts may be stacked on top of each other toprovide thick articles which are then subjected to a bondingtemperature. The nonwoven products may be formed such that the filamentsare arranged therein to have fiber-on-end, fiber-on-side or randomalignment. Also they may, following or during bonding, be laminated tovarious backing materials for additional support or for furtherprocessing into still other textile products.

The products of this invention are useful for processing into a widevariety of nonwoven, woven, knitted and tufted textiles for a variety ofapplications, but are particularl suitable for the manaufacture ofbonded, nonwoven textiles, either quilted or unquilted. They are alsosuitable for use in making pillow fillings, fillings for sleeping bags,cushions, quilts, comforters, coverlets, mattresses, mattress pads,mattress toppers, furniture and auto upholstery, bedspreads, pilefabrics for industrial and apparel uses, blankets, womens robes, sportjackets, car coats, interlinings, outerwear, floor covering materials,tiles, carpets, bath mats, molded articles, and the like.

For the preparation of pillows, cushions and other articles it is alsoentirely practicable as shown in FIG- URE 3 to use the unbonded assemblyfor filling a fabric,

or other covering followed by heating the entire structure to effectbonding.

Advantages summarized A most fundamental advantage of the novel assemblyof the invention is that it can be formed to a desired shape by thetextile converter and bonded, by mere application of heat, with littleor no change in shape. Another advantage of the invention is that itprovides an assembly of filaments which are specially adapted to theformation of nonwoven textile structures having a combination ofoutstanding properties. When the assembly is fashioned into a textilearticle and then subjected to the thermal activation temperature of thelower-melting component, a bonded product is obtained in which the bondsare uniformly distributed throughout the three dimensions thereof. Thispermits the manufacture of nonwoven products having a combination ofhitherto unobtainable properties; namely, the textiles can have a lowerdensity, and they tend to be softer and have better drape propertiesthan nonwoven textiles of the prior art. Products having a density ofless than 1.5 lbs./ft. in many cases as low as 0.2 lb./ft. and below,are obtained. By virtue of a relatively uniform distribution of bondpoints throughout the three dimensions thereof, a high degree ofheight-retention and load support properties are obtained in theproduct. The uniform three-dimensional bonding provides a superiorresistance: to dimensional changes, resistance to clumping, resistanceto fiber leakage, and resistance to matting after repeated washings ordry cleanings. The invention is also useful for making bonded yarns forwoven, knitted, and tufted fabrics which will show less pilling andwhich will require less yarn twist in manufacture.

where L =the length of the coated filament in inches when subjected to aload of 2 mg./denier per filament, based upon the denier of only thefilamentary component; and L =the length of the filament in inches underthe same load after exposure to a temperature above the polymer melttemperature of the lower-melting component but below the fiber sticktemperature of the structural fiber component. For purposes of themeasurement, the temperature selected will usually be the minimumtemperature required to sufficiently soften or melt the lower-meltingcomponent to form effective fiber-to-fiber bonds. In the examples whichfollow, the temperature selected will be the same as the bondingtemperature. Conveniently, the measurement is made after exposure to atemperature between 1 and 20 C. above the polymer melt temperature.(Only a nominal difference in RC would be experienced Within thisrange.) The values of L and L,, are measured on a cathetometer while theload is applied to the filament on a Model LG Precision Balance (FederalPacific Electric Co.). An average is taken from measurements on fivefilament specimens.

Polymer melt temperature, PMT, is in the case of essentially amorphousor essentially crystalline polymers, the temperature at'which a sampleof the lower melting component leaves a molten trail when moved across aheated metal surface with moderate pressure. Polymers containingsubstantial amounts of amorphous and crystalline regions are moreaccurately tested for polymer melt temperature by ascertaining themelting of the last crystal of a sample when heated, e.g. on a hot stagemicroscope using crossed optical polarizers (in the literature this issometimes referred to as' indicative of crystalline. melting point).

Fiber stick temperature is described in Beaman and Cramer, J. PolymerScience, 21, .228 (1956).

Crimp frequency is determined by counting, under a magnifying glass, thenumber of crimps in the fiber while under a tension of 2 mg./ denier.The fiber is then extended until it is just straight (observed visually)and the extended length is measured. The crimp frequency, expressed ascrimps per inch, based on the extended length of the filament, iscalculated. An average is taken from measurements on five filamentspecimens.

Crimp index is determined by measuring the length of a filament firstunder a tension of 2 mg./denier and then under a tension of 50mg./denier. Crimp index is the change in length expressed as apercentage of the uncrimped length. An average is taken frommeasurements on five filament specimens.

Drape test, or Flexural Rigidity is measured according to ASTM D-1388-55T.

Softness test, ILD 25 (Indentation Load Deflection at a deflection of25%), involves measuring the load in pounds necessary to produce a 25%deflection of the sample. The load in lbs. is calculated on the basis ofa 50 square inch deflection area. The testing apparatus consists of aSchiefer Compressometer (Frazier Precision Instrument Co., SilverSpring, Md.) modified for use as a dead-weight thickness gauge. Theprocedure consists .of placing a sample on the gauge, reading theinitial thickness and then adding weights to the presser foot of thegauge until the sample is deflected 25%.

The following examples further illustrate the practice of the invention.Parts and percentages are by weight unless otherwise stated.

EXAMPLE I Polyethylene terephthalate polymer (abbreviated 26- T) ismelt-spun, drawn and crimped in accordance with Kilian US. Patent3,050,821 to produce filaments of 4 denier/filament. The procedureinvolves air quenching the filaments as they exit from orifices of aspinneret, drawing the filaments in superheated steam and then relaxingthe tension. U-pon release of the tension of drawing, it is observedthat the filaments exhibit a high level of three-dimensional crimp,referred to as a reversing helical crimp. The filaments from severalspinnerets are combined to produce a filamentary tow having a totaldenier of about 50,000.

After crimping, the tow is annealed in an air oven at 160 C. for oneminute to relax the filaments, to eflect further crimping and to lowerthe retractive coefficient. The tow is then opened by hand from acylindrical to generally fiat tow. This is then deregistered to separatefilament groups. For this purpose, there are used two sets of positivelydriven nip rolls of the type more particularly described in Dunlap eta1. U.S. Patent 3,156,016. These pressure nip rolls have a diameter of 2/8 inches and are 14 inches long. In each set of rolls, one has a seriesof helical threads whose ridged surfaces are 0.017 inch wide. The otheris a smooth-surfaced elastomer covered roll. Upon pulling the tow undertension through the nips of the rolls, married groups of adjacentfilaments are rendered out of phase with one another to deregister thecrimps.

The deregistered tow is then given a second annealing treatment at 227C. for 15 minutes in an air oven. This is just below the fiber sticktemperature of the 2G-T which is 230 C. and well above thesecond-order-transition temperature of 80 C.

The opened and deregistered tow is then passed through a dip tankcontaining a by-weight solution of a copolyester in 1,1,2trichloroethane and then squeezed free of excess solution. Apparatusgenerally similar to that of FIGURE 5 is used for this purpose. Thecopolyester has a polymer melt temperature of 208 C. and is a copolymerof 79 parts by-weight ethylene glycol terephthalate and 21 partsethylene glycol isophthalate (abreviated 2G-T/2G-I). The tow is found topick up 10% of the lower-melting copolyester component, based onfilament plus copolyester. The tow is dried at 65 C. under minimaltension to produce an integral, flat bonded ribbon-like structure whichis continuous in length and has a cross-section dimension of 5 by 0.1inches.

The ribbon-like structure is next reduced to 2 inch length sections bycutting it in the transverse direction using a Pacific Converter. Thefilaments at this stage have a crimp index of 20, a crimp frequency of14 crimps per inch and a retractive coefficient of only 6.

The adhesive-bonded fibrous sections are next treated to mechanicallydistribute the filaments, break the bonds and thereby obtain a highlyuniform, low-density assembly of individualy distinct, staple-lengthfilaments. For this purpose, carding of the fibrous sections is effectedon a commercial garnett carding machine.

The unbonded assembly of filaments produced by carding is cross-lappedto form a batt whose dimensions are 23 by 17 by 0.79 inches. The batt isthen bonded in an air oven under the conditions indicated in Table 1. Asfurther indicated therein, only modest densification occurs during thebonding step-the overall density being extremely low. Mostimportantly,the bonded nonwoven product so obtained is uniformly bonded throughoutsuch that its properties are also constant in all portions.

TABLE 1 Batt bonding temp. C.) 227 Batt bonding time (mins) 15 Density(lbs./ft. )-carded 0.11 Density (lbs./ft. )-bonded 0.18 Softnes, ILD 25%(lbs) 0.6 Drape, flex. rig (mg-cm.) 312 EXAMPLES II-V A bondedribbon-like structure is produced as in Example I except that bothbefore deregistration and after clipping (omitting annealing at 227 C.)the tow is annealed at 221 C. for 5 minutes under minimal tension in anair oven rather than at 227 C. for 15 minutes. The ribon-like structureis then cut to 3-inch long fibrous sections on a Beria cutter.

The fibers have a crimp index of 26%, a crimp frequency of 15 crimps perinch and a retractive coefiicient of 3.

The fibrous sections are opened using a Kirschner opener having athree-blade beater bar.

The annealed staple fibers are then carded into a web on a Proctor &Schwartz 740 carding machine to effectively break up interfilament bondsand evenly distribute the filaments. The card web is then fed onto acard cloth cylinder which separates the fibers in the web from oneanother. The fibers are then transferred from the cylinder to an airstream by jets of air and collected on a perforated belt having a vacuumslot underneath it. Four batts of varying density are prepared.

The air-laid batts are then bonded at 218 C. for five minutes in an ovenhaving forced air directed upward against the batt so as to minimize thetendency for compaction to occur. The properties of the carded batts andbonded structures are shown in Table 2.

EXAMPLES VI-VII Helically crimped, deregistered 2G-T filaments areproduced in accordance with Example I except that the drawn 13 tow has atotal denier of about 860,000 and no heat is applied to the fibers afterdrawing. The tow is then sprayed with a 6% solution of 79/21 2G-T/2G-Iin 1,1,2 trichloroethane to produce a bonded tow structure having a2GT/2GI content of 9% based on the total weight of fiber and 2G-T/2G-I.The bonded tow is then divided into two parts a Control and VI/VII. TheControl part receives no heat treatment and part VI/VII is annealed at215 C. for 10 minutes under minimal tension in an air oven. Both partsare then cut to 2" long fibrous sections using hand shears.

The Control part filaments, which have had no annealing, have a crimpindex of 15%, a crimp frequency of 9 crimps per inch and a retractivecoefiicient of 37. The part VI/VII filaments have a crimp index of 28%,a crimp frequency of 13 crimps per inch and a retractive coetficient of3. The bonded fiber sections from each of the parts are separatelycarded into batts on a sample card to uniformly distribute the staplefilaments and to break up the filament-to-filament bonds. A pair ofbatts are formed from the Control part item to have a density of 0.3 and0.6 lb./ft. respectively, after carding. A similar pair of batts isformed from the part VI/VII item.

The four batts are then bonded in an air oven at 218 C. for minutes. Asshown in Table 3, the Control part lbatts, whose fibers had noannealing, lose 25-50% of their bulk during bonding. However, the partVI/VII batts, Whose fibers were annealed at 215 0., show little or nodensification during bonding.

TABLE 3 Control Part VI/V II Annealing temp. C.) None 215 Bonding C.)218 218 SampleA SampleB SampleVI SampleVII The procedure of Example I isrepeated except that a sample carding machine is used to form thenon-woven batt and just before carding, quantities of monocomponent 2G-Tstaple which had been annealed at 175 C. for 2 minutes then again at 227C. for 15 minutes, in tow form, prior to its being out, are blended withthe coated staple. The monocomponent 2G.T fibers are of 2-inch (5.08cm.) staple length, are 4'denier per filament, and have a crimp index of32, a crimp frequency of 11 and a retractive coetficient of 1. Blendscontaining 40%, 80% and 95% of the monocomponent fibers are used andvery soft, lightly-bonded, low-density structures are obtained. Battdensities are shown in Table 6.

Nylon (66) tow having a filament denier of three total denier of 430,000and a stufiing-box type of crimp is deregistered on the threaded-rollmachine of Example I, then sprayed with a 5% solution of a copolyesterdissolved in two parts methylene chloride and one part 1,1,2-trichloroethane to provide a content of 15 by weight, of thecopolyester. The composition of the copolyester (abbreviated 2G-T/2G10)is a 55/45 weight ratio of ethylene terephthalate and ethylene sebacateunits and its polymer melt temperature is 159 C. The tow is then cut to2-inch (5.08 cm.) staple, annealed at 180 C. for 5 minutes in an airoven and carded on a sample carding 14 machine. The properties of thefiber are listed in Table 7. The carded batt is bonded at 160 C. for 5minutes; batt properties are shown in Table 7.

The procedure of Example IX is repeated except that conventionalpolyacrylonitrile tow (fiber stick temperature is 231 C.) having afilament denier of 3 and a total denier of about 500,000 is used. Fiberand batt properties are listed in Table 8.

TABLE 8 Fiber properties:

Crimps per inch 9 Crimp index (percent) 9 RC. 5 Batt density, lb./ft.(g./cm.

Carded 0.22 (0.004) Bonded 0.40 (0.006)

EXAMPLE XI The procedure of Example VI is repeated except that thelower-melting component is a copolymer of vinyl chloride and vinylacetate (about 87:13 weight ratio, polymer melt temperature of 136 C.)and the temperature used for the tow annealing :and batt-bonding stepsis C. Carded and bonded batts having density properties similar to thoseobtained in Example VI are produced.

EXAMPLE XII The procedure of Example XI is repeated except that thelower-melting component is an alcohol soluble terpolymer (polymer melttemperature of C.) formed by condensing caprolactam, hexamethylenediamine, adipic acid and sebacic acid, such that there are substantiallyequal portions of polycaproamide, polyhexamethylene adipamide andpolyhexamethylene sebacamide in the terpolymer, the solvent is an 80/20ethanol/Water mixture by volume and the temperature used for thefiber-annealing and batt-bonding steps is C. Results similar to ExampleXI are obtained.

The invention has been particularly described with reference toapplications in which the bonded product is used for cushioning andfilling purposes and as a pile fabric. In these or other uses natural orsynthetic resins or elastomers may be applied by suitable methods to theself-bonded products of the invention to produce coated substrates,laminates, bonded felts and the like.

'What is claimed is:

1. Method for producing a thermally self-bendable assembly ofindividually distinct, staple-length filaments comprising the steps of(1) collecting into a continuous length bundle a plurality of filamentscomprising an oriented filamentary component of a fiber-forming,synthetic, organic polymer (2) crimping said filaments to provide anaverage crimp frequency of at least 3 crimps per inch and an averagecrimp index of at least 5%, (3) separating the crimped filaments fromone another, (4) applying to said crimped, separated filaments, withoutsubstantially removing crimp therefrom, a coating of a lower-meltingsynthetic thermoplastic polymer component to thereby provide acontinuous ribbon-like structure, said lowermelting component having apolymer melt temperature which is at least 70 C. but is below the fiberstick temperature of the filamentary component, (5) transversely cuttingsaid continuous ribbon-like structure to Provide fibrous sections ofstaple-length filaments, (6) opening said sections, mechanicallydistributing said staple-length filaments and providing a low-densityassembly of in dividual- 1y distinct filaments having throughout thethree dimensions thereof an essentially constant weight ratio of saidfilamentary component to said lower-melting component, (7) it beingfurther provided that at least prior to the preparation of saidlow-density assembly of step (6), above, said filamentary component isannealed at an elevated temperature in a substantially relaxed state toprovide a maximum retractive coeflicient of about 30.

2. Method according to claim 1 wherein the said annealing temperature isin excess of the second-order transition temperature of said filamentarycomponent.

3. Method according to claim 1 wherein said lowermelting component isapplied by dipping said bundle in a solution of said lower-meltingcomponent.

4. Method according to claim 1 wherein said polymer melt temperature isWithin 5 to 50 C. of said fiber stick temperature and said retractivecoefiicient does not exceed about 15.

5. Method according to claim 1 wherein said filamentary component ispolyethylene terephthalate andsaid temperature in excess of said polymermelt temperature but below said fiber "stick temperature and coolingsaid assemblyto thereby bond said filamentary components.

References Cited UNITED STATES PATENTS 3,391,048 7/1968 Dyer et al.156-181 XR 3,177,644 4/1965 Aspy et a1. 28-75 XR 3,255,506 6/1966 Fritz;

PHILIP DIER, Primary Examiner US. ,Cl. X.R.

